In the search for novel materials for organic light-emitting diode (OLED), organic field emission transistor (OFET) and emissive liquid crystal display (eLCD) applications, a number of basic structure considerations are necessary:                Materials should possess a highly conjugated structure, with a long UV wavelength absorbing chromophore. This facilitates efficient excitation of the molecule, either by photons or electrons, giving rise to photo- or electroluminescence.        In order to be compatible with calamitic liquid crystalline media, and in order to be efficient emitters of polarised light, either by photo or electroluminescence, materials should ideally be rod-shaped molecules.        The rod-like molecules should comprise lateral substituents in order to modify the melting point, the nature of mesophases and the solubility in common solvents or liquid crystal hosts.        
It is generally known in LC structure property relationships that lateral substituents, such as halo, alkyl, alkoxy groups, in calamitic LC's reduce the melting point, modify the mesophase and improve the solubility. See for example Gray, G. W., Hird, M. & Toyne, K. J., 1991, Mol. Cryst. Liq. Cryst., 204, 43. Additionally it is known that for OLED polymers the lateral chains improve solubility as well as acting as a modifier to the electroluminescence properties. See for example Kraft, A., Grimsdale, A. C. & Holmes, A. B., 1998 Angewandte Chemie Intl. Edn. Engl., 37, 402-428.
There are many examples of liquid crystals with extended conjugated structures in prior art. Many of these find use as additives for high birefringence mixtures, useful especially in the infrared range of the electromagnetic spectrum, like for example the diphenyldiacetylene LC compounds disclosed in U.S. Pat. No. 6,312,618.
There are additionally prior art references to the use of fused ring structures as molecular components of liquid crystals, especially naphthalenes. In the emerging field of organic charge transport materials, the work of Hanna is especially relevant, as it details the advantage of smectic LC ordering on charge transport in phenyl naphthalene structures. See for example Y. Toko, M. Funahashi, J. Hanna, Japan. Proceedings of SPIE—The International Society for Optical Engineering (2003), 4800 (Organic Light-Emitting Materials and Devices VI), 229-237; N. Yoshimoto, J. Hanna, Adv. Mater. 2002, 14(13-14), 988-991; H. Maeda, M. Funahashi, J. Hanna, Materials Research Society Symposium Proceedings (2000), 598 (Electrical, Optical, and Magnetic Properties of Organic Solid-State Materials V), BB3.61/1-BB3.61/6.
Additionally US 2001-0048982 teaches emissive LCD devices that include phenyl naphthalene materials.
Time of flight measurements show improvements to charge carrier mobility as smectic order increases. The reason for improved charge mobility is thought to be that smectic ordering allows closer packing of the planar aromatic cores.
However, many prior art materials are unsuitable as components of OLED or other optoelectronic devices, because the extent of their conjugation is limited, resulting in poor excitation properties for efficient electroluminescence.
The use of polymerisable LCs, also known as reactive mesogens (RM), for OLED and OFET applications, in particular as a means of producing polarised emission, has also been reported in prior art. For example, US-A-2003/0018097 discloses the use of a direactive RM comprising a 9,9′-dialkylfluorene group that is substituted in 2- and 7-position with a 5-phenyl-thiophene-2-yl group. Bacher, Bradley et al., J. Mat. Chem. 1999, 9, p. 2985 disclose a distyrylbenzene RM and its use for a polarised electroluminescence (EL) device. O'Neill et al., J. Appl. Phys. 2003, 93(3), p. 1465 disclose the use of and references contained within, disclose the use of some reactive mesogen species for polarised light emission.
However, the RMs cited in these references comprise an acrylate or 1-vinyl-allyloxycarbonyl group as polymerisable group, which can be disadvantageous for efficient OLED emission, as the carbonyl group is known to quench electroluminescence (see List et al., Adv. Mater. 2002, 14(5), p. 374). Additionally, these references report that residues of the photoinitiator used for polymerisation of the RMs can have a detrimental effect on electroluminescence. Meerholz et al., Nature 2003, 421, p. 829, however, report that it is possible to use a cationic photoinitiator process to produce a cross linked polymer OLED based on oxetane photopolymerisable groups without detriment to the OLED electroluminescent properties.
One aim of the present invention is to provide novel mesogenic or liquid crystalline compounds with a rod-shaped molecular structure which are optionally polymerisable, which do not have the drawbacks of prior art or do exhibit them to a lesser extent, have improved properties, and are especially suitable for liquid crystal, semiconducting and light-emitting applications, like LCD, eLCD, OLED and OFET devices.
The novel compounds should fulfill the above-mentioned basic structure requirements for OLED, OFET and eLCD use. Preferably they should exhibit a liquid crystal phase over a broad temperature range, allow close packing in a highly ordered mesophase, and show good charge transport and light emission properties.
Another aim of the invention is to extend the pool of materials suitable for LCD, OLED and OFET uses that are available to the expert.
Another aim of the invention is to provide advantageous uses for the novel compounds, such as liquid crystal, light emitting and semiconducting materials and devices, in particular LCDs, eLCDs, OLEDs and OFETs, anisotropic polymers, optical, electrooptical, decorative, security, cosmetic, diagnostic, electric, electronic, charge transport, semiconductor, optical recording, electroluminescent, photoconductor and electrophotographic applications.
Another aim of the invention is to provide improved LC, OLED and OFET materials, polymers and devices with that do not have the drawbacks of LC media known from prior art.
Another aim of the invention is to provide new oligo- and polymers for use as semiconductors or charge transport materials, which are easy to synthesize, have high charge mobility, good processibility and improved oxidative stability.
Other aims of the present invention are immediately evident to the person skilled in the art from the following detailed description.
The inventors of the present invention have found that the above mentioned drawbacks can be overcome by providing novel mesogenic anthracene derivatives as claimed in claim 1. These compounds have advantageous properties and are especially suitable for use in LCD, eLCD, OLED and OFET devices.
The compounds according to the present invention, which include anthracene as a major component of the aromatic core, pack in a very efficient manner and produce very efficient charge transport, thus making them good candidate materials for OFET use. Additionally, the anthracene moiety is highly fluorescent on irradiation with UV light, both as a solution and as a thin solid film.
Furthermore, the inventors have found that monomers, oligomers and polymers based on anthracene modified with photostabilising substituents in 9- and 10-position are suitable as semiconductors or charge transport materials. The presence of an alkoxy group R in the 9- and 10-positions of the anthracene ring system increase the solubility and thus the processability of the polyanthracenes.
EP 1 090 911 A2 discloses a bis(aminostyryl) anthracene compound emitting yellow or red light. U.S. Pat. No. 6,495,274 discloses an OLED device comprising a bis(aminostyryl) anthracene compound. However, these materials are not likely to be mesogenic as they do not have terminal chains, additionally they cannot be cross linked, as they have no reactive component. This would lead to serious deficiencies in device processing.